A “law-enforcement sensitive” document telling cops how to detect explosive materials in vehicles was left outside a Midtown police station in a garbage can — where it was scooped up by a passing Internet blogger.

The eight-page memo warns cops to watch out for drivers who show “obvious shaking” or “hair on arms standing on end” when stopped by police, according to a copy posted by the Web site Animal New York.

It also says to be on the lookout for “wire and tape stored in vehicle,” “fresh bodywork,” “fresh undercoating” or a “false compartment that are not part of the vehicle design.”

“We would have preferred it was disposed of more discreetly, but its discovery by a Dumpster-diver posed no threat to the public or anyone else,” said Deputy Police Commissioner Paul Browne.